1. Field of the Invention
The present invention relates to angular velocity detection devices to detect angular velocities by making use of a Coriolis force.
2. Description of the Related Art
An angular velocity detection device includes a vibration body having a plurality of vibration modes. In a state in which the vibration body vibrates in a predetermined vibration mode (drive vibration mode), the angular velocity detection device detects vibrations in another vibration mode (detection vibration mode) generated in the vibration body due to action of an angular velocity causing a Coriolis force to work, and then detects the angular velocity.
Here, an example of the structure of a known angular velocity detection device will be described. Hereinafter, an axis along a direction perpendicular or substantially perpendicular to a plate surface of the angular velocity detection device (thickness direction) is taken as a Z axis of the orthogonal coordinate system. Further, two axes perpendicular or substantially perpendicular to each other along the plate surface are respectively taken as an X axis and a Y axis of the orthogonal coordinate system.
FIG. 8A is an X-Y surface plan view of an angular velocity detection device 201 according to a known example (for example, see Japanese Unexamined Patent Application Publication No. 2009-74996).
The angular velocity detection device 201 includes tuning forks 202A, 202B, 202C, and 202D, a base portion (supporter) 203, beams 204A, 204B, 204C, and 204D, and a frame body 205. The base portion 203 is disposed at the center of the angular velocity detection device 201, and fixed to an external structure. The frame body 205 is formed in a frame shape and encloses the base portion 203 within the frame. The beams 204A, 204B, 204C, and 204D extend from the base portion 203 in equiangular directions and are respectively connected to four corners of the frame body 205. The tuning forks 202A, 202B, 202C, and 202D respectively extend, from the base portion 203, between the beams 204A and 204B, 204B and 204C, 204C and 204D, and 204D and 204A, and each leading end thereof forks into two branches.
In the angular velocity detection device 201, in a state of vibrating in a predetermined vibration mode (drive vibration mode), when angular velocities about the X and Y axes act and cause Coriolis forces to work, vibrations in independent vibration modes (detection vibration mode) are generated at each of the X and Y axes. Accordingly, by detecting the vibrations in the respective detection vibration modes, the angular velocities about the X and Y axes can be detected. However, angular velocities about three axes cannot be detected by a single angular detection device. Accordingly, in order to detect angular velocities about the three axes, it is necessary to combine and use a plurality of angular velocity detection devices.
As such, an angular velocity detection device capable of detecting angular velocities about the three axes only by the single angular velocity detection device is also proposed.
FIG. 8B is an X-Y surface plan view of an angular velocity detection device 401 (for example, see Japanese Unexamined Patent Application Publication No. 2012-177610) according to a known example capable of detecting angular velocities about the three axes only by the single angular velocity detection device 401.
The angular velocity detection device 401 includes a frame 402, a base (base portion) 403, connectors 404, and pendulums (mass bodies) 405A, 405B, 405C, and 405D. The frame 402 is formed in a frame shape. The pendulums 405A, 405B, 405C, and 405D are disposed at the inside of the frame 402, and respectively extend from the four corners of the frame 402 being directed toward the center of the angular velocity detection device 401. The base 403 is formed in a frame shape, encloses the frame 402, and is fixed to an external structure. The connectors 404 connect the frame 402 and the base 403 to each other. In the angular velocity detection device 401, in a state of vibrating in a predetermined mode (drive vibration mode), when angular velocities about the X, Y, and Z axes act and cause Coriolis forces to work, vibrations in independent vibration modes (detection vibration mode) are generated at each of the X, Y, and Z axes. This makes it possible to detect vibrations in the respective vibration modes and consequently detect the angular velocities about the X, Y, and Z axes.
In general, angular velocity detection devices are required to be compact and have highly excellent detection sensitivity. However, due to advancement in miniaturization of angular velocity detection devices, resonant frequencies of the angular velocity detection devices become higher so that the detection sensitivity to angular velocities tends to be lowered. For example, in a digital camera or the like configured to detect a camera shake by making use of an angular velocity detection device, there is a case in which a camera shake detection sensitivity is decreased because of a large difference between a resonant frequency of the angular velocity detection device and a frequency of the camera shake. Accordingly, angular velocity detection devices are required to have a low resonant frequency even if the devices are miniaturized.
In order to lower the resonant frequency in an angular velocity detection device, it is effective to make a length of a beam that is connected to a mass body longer. For example, in order to lower the resonant frequency in the angular velocity detection device 401 shown in FIG. 8B, it is necessary to make the lengths of the beams of the pendulums 405A through 405D longer. However, because the connectors 404 and the base 403 are arranged at an outer side portion of the frame 402 that is arranged at an outer side portion of the pendulums 405A through 405D, the beams of the pendulums 405A through 405D cannot be lengthened unless the base 403 and the frame 402 are made larger together. As such, it is necessary to make the overall angular velocity detection device 401 larger so as to suppress (lower) the resonant frequency.